What kind of machine you need would depend on what kind of music you wanna make. If you are interested in electronic music, with lots of plugins and synths you would be heavily interested in the performance of the computer - RAM and cpu power. You would also need to research the capabilities of the DAW you use. Not all DAW's can access multiple cores and if you end up with such a DAW, a computer with 4 cores each running at 2GHz would be less powerful than one core running at 3GHz.
Read this article to have an idea of that:
http://www.soundonsound.com/sos/jan08/articles/pcmusician_0108.htmIf you are interested in recording live music, and especially acoustic music, which would require less plugins, no synths etc, then you would be more interested in hardware than the computer. Most readily available computers are built to a standard now that can easily support music. I'm using a simple dual-core machine with just 4GB of RAM and only a 32bit version of cubase on win xp. I can easily record up to 30 or more tracks all with a number of plugins and processing going on.
Far more important than the actual computer are the monitors (speakers) and audio interface. If you are buying from a computer shop (not a music shop) then the bundled sound cards they do wont cut it.
You need to think about how many inputs/outputs do you need?, do you need midi? do you need good preamps?
Theres a useful tool here to help you decide:
http://www.recordingreview.com/soundcard/soundcard_wizard.phpTBH, I see no reason to spend that amount of money on a pc just for recording. I picked up my pc off ebay for £100 a bout 3 years ago. I've upgraded the RAM and added a harddrive since then. My audio interface cost more than that.
What could be useful is going onto a large music retailers site like Dolphin music or Thomann and seeing what bundles they do - often they might have offers on computers bundled with DAW's and interfaces or computers and monitors etc etc
As for DAW's - I would save money and get Reaper. It's excellent - I would've gone that road if I hadnt already being using cubase, and I'm in fact starting to migrate across to the 64bit version of reaper on windows 7 as its cheaper than upgrading to cubase 6.
You'll have enough to spend on an interface and monitors, preamps and microphones (if you don't already have them).
Of course if you have all that then go crazy and buy an awesome pc/mac